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Securing OpenVPN With A One Time Password (OTP) On Ubuntu

"So, you got yourself a nice OpenVPN box. People need to login
with their certificates but... if their laptop is stolen anyone
could login. Sure, you could add password login but thats a bit
outdated. The solution for this is using a OTP (one time
password).

"This technique is being used by a lot of large corporations
including banks. This tutorial shows you how to configure OpenVPN
to add additional security.

"This assumes you already have OpenVPN configured and working
properly."